JPH0675823B2 - Grinding machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a grinding apparatus capable of mirror-grinding a hard and brittle material, particularly a metal bond grindstone using cast iron as a bond material.
The present invention relates to a grinding apparatus that performs grinding while dressing by an electric field effect.

(Prior art and its problems) Cast iron fiber bonded diamond grindstone (hereinafter CIFB-D
A grindstone: Cast Iron Fiber Bonded-Diamond) is a type of fiber-reinforced composite material made by mixing diamond abrasive grains and carbonyl iron powder into a cast iron fiber base material and sintering it. The abrasive grains are held by a strong bonding force. And has been studied to realize high (removal) efficiency grinding of hard and brittle materials such as ceramics.

The basic grinding action of the conventional grinding wheel called so-called eclipse type is different from the fact that a constant cutting edge like cutting cuts to the end, unlike the abrasive grains, binding material and holes that make up the grinding wheel. Acts, the abrasive grains and the bonding material are crushed during processing, and new cutting edges and holes are always self-generated to remove the work material. However, the CIFB-D grindstone is a typical so-called blind type, and because of the diamond abrasive grains and its strong bond material, the spontaneous action of the abrasive grain cutting edges and holes as described above does not occur, Further, even if a dressing method using a WA stick grindstone made of aluminum oxide abrasive grains is used, there is a problem that a sufficient protrusion amount of the abrasive grains, which is a main condition for grinding, cannot be obtained. Therefore, recently, a spark dressing method has been developed which combines dressing and grinding so as to remove not only the work material but also the bond material of the main grindstone by the spark generated when the difficult-to-cut material is forcibly ground. However, in the actual production line, there is no such grinding process that simply requires a high removal amount, and there are still few processing machines that have rigidity and output that can withstand a strong grinding force, and rather polishing such as lapping. Applied research to the process was desired.

The inventors of the present invention have used CI for the mirror polishing of silicon, which is an electronic material.
With the aim of applying the FB-D grindstone, research has been repeated and various studies have been conducted on conventional dressing methods, focusing on the fact that a good glossy surface cannot be obtained if the amount of protrusion of the abrasive grains of the grindstone is insufficient. It was In particular, the smaller the abrasive grains in order to obtain a good mirror surface, the more difficult the dressing of the CIFB-D grindstone becomes, and if the mechanical dressing using the conventional WA stick grindstone is carried out, sufficient abrasive grains will be obtained. There was a problem that fine abrasive grains would be dropped soon after the protrusion was obtained. In addition, we found that a slurry surface dressing method was applied to the main grindstone by performing grinding while supplying loose abrasive grains, and that we could obtain a glossy surface that could not be obtained conventionally by applying the electric discharge grinding method. By combining a fine abrasive grain CIFB-D grindstone and a dressing method by electrolysis during the grinding process, it has been possible to realize good mirror surface grinding of a silicon wafer.

(Means for Solving the Problem) The present invention provides a liquid receiving portion for receiving a supplied weakly conductive grinding fluid, a metal bond grindstone using cast iron as a bond material,
The entire grinding work surface of this grindstone is moistened in the grinding liquid received by the liquid receiving part, and the working surface is temporarily in partial contact with the workpiece. A metal bond grindstone, a grinding work surface of the metal bond grindstone. Means for moving the grinding work surface on the grinding surface of the work piece relative to the work piece, and the metal bond grindstone as an anode, and being wet with the grinding liquid. It is characterized in that a pulse direct current power source is provided for applying a pulse direct current voltage while the electrode is used as a cathode while the slidable motion is being performed.

(Operation) The abrasive grain protrusion forming process and the grinding operation by the electrolytic dressing method that occur in the apparatus of the present invention will be described in detail below.

FIG. 5A is a schematic diagram showing a cross-sectional shape of a CIFB-D grindstone before use, in which diamond abrasive grains are appropriately distributed in a cast iron fiber, a bond material, and pores. In general, a grindstone before use has a rough uneven surface and a runout of a shaft center, so it is necessary to perform truing according to the processing purpose. FIG. 5B is a schematic diagram showing a cross-sectional shape of a CIFB-D grindstone that has been trued and dressed by WA stick grindstone grinding. As mentioned at the beginning, this grindstone does not grind the abrasive grains like the conventional grindstone, so the surface is smoothed as shown in Fig. 5B, but the cutting edges and holes formed by the abrasive grains occur. Not not. Therefore, when grinding is started with this surface condition, at first, it is possible to grind by protruding some diamond abrasive grains, but within a short time, other than abrasive grains due to wear reduction of the abrasive grains, clogging, etc. The bond material and cast iron fiber of (1) come into contact with the workpiece, and clean grinding cannot be performed.

Contrary to electroplating, there is known an electropolishing technique in which the surface of the work piece is melted and metal is deposited on the cathode when the work piece is energized in the electrolytic solution as an anode. The CIFB-D grindstone has conductivity because it contains cast iron fiber and iron powder, and the coolant (grinding fluid) is weakly conductive. Therefore, when electricity is applied between the grindstone and the coolant from the power source, the grindstone will be electrolyzed. The metal portion on the surface is melted and the non-conductive diamond abrasive grains are projected.

FIG. 4A is a schematic diagram showing a cross-sectional shape of the CIFB-D grindstone dressed from the surface state of FIG. 5B by a strong electrolytic effect in the present invention. The conductive metal part is dissolved by electrolysis, while the non-conductive diamond abrasive grains remain as they are, and a protrusion amount capable of grinding is obtained.
The desired abrasive grain protrusion amount is the applied voltage of the power supply device, the current,
It can be set according to the time, the conductivity of the grinding fluid, and the like.

The grinding action of the CIFB-D grindstone of the present invention on a workpiece is
Unlike the conventional grinding by crushing abrasive grains, the diamond abrasive grains in the main grindstone have a high degree of acting as a cutting blade, and the work is removed by an action close to cutting. Therefore, the abrasive grains wear out while removing the workpiece.

FIG. 4B is a schematic diagram showing that, in the present invention, the amount of protrusion of abrasive grains is reduced during the grinding process, and grinding debris is accumulated between the abrasive grains to cause clogging. In the present invention, as the cutting process progresses, grinding debris is removed by the weak electrolytic effect, and the dressing can be automatically performed during the actual process without stopping the operation until the grinding process is completed.

(Effect of the Invention) According to the present invention, silicon which has been conventionally considered difficult to process,
In addition to hard and brittle materials such as ferrite and ceramics, cemented carbide, various steel materials, metal magnetic materials, etc. using conductive CIFB-D and CIFB-CBN (when grinding iron-based materials) grindstone, etc. By sequentially performing the dressing effect by strong electrolysis and the electrolytic grinding process by relatively weak electrolysis,
It has become possible to obtain extremely good mirror surfaces and smooth flat surfaces that have not been obtained until now with high efficiency and high speed. In addition, it can be applied to abrasive grain processing such as super finishing other than grinding, honing, lapping, etc., and can perform not only mirror finishing but also heavy grinding, and it is possible to reasonably achieve high removal efficiency.

The electrolytic dressing method of this conductive grindstone does not require the conventional mechanical dressing because it can perform unmanned operation at high speed with high accuracy by controlling the electrolytic conditions. Since the dressing of the grindstone is easy and the dressing can be performed without being influenced by the shape of the grindstone, the invention has high flexibility. As for the electrolyte, even a commercially available water-soluble grinding fluid diluted with tap water has weak conductivity, so it is economical not requiring any special additives, and it is also possible to worry about machine corrosion due to the electrolyte. Absent.

The configuration of the electrolytic dressing device does not require major remodeling because the existing processing machines are combined and parts are attached in an attachment manner. The power supply device for electrolysis can also be applied to electric discharge truing, and after the electric discharge truing on the machine, it is possible to immediately shift from electrolytic dressing to electrolytic grinding processing, eliminating complicated labor at each processing stage, surface roughness and grinding resistance. It is possible to realize semi-automation of grinding by equipping with equipment that measures the resistivity and temperature of the grinding fluid, the resistivity of the workpiece, etc. in-process and always controlling the optimum amount of protrusion of abrasive grains.

As described above, in the field of grinding and polishing, the present invention can be semi-automatically processed in-process regardless of the type and shape of the grindstone as long as it is electrically conductive. It is very efficient, long-lived, economical and has a wide range of application fields.

(Example) The following table shows the specifications of the grinding system used to carry out the present invention.

In this embodiment, a fine rotary CIFB-D grindstone (# 4000) is attached to a precision rotary surface grinder for the purpose of mirror-grinding silicon, which is a hard and brittle material, and an existing wire-cut pulse DC for generating electrolysis is attached to this. A power supply was used. The grinder uses static pressure bearings for both the grindstone shaft and the table rotary shaft, and has high rigidity because it is an experimental machine, and the coolant (grinding liquid) is discharged from the center of the magnet shaft. Greatly reduces clogging. Further, the applied voltage, maximum current value, and frequency of the power source can be arbitrarily set. Further, the coolant tank used for electrolytic grinding, the power supply brush, and the like have been improved. Commercially available coolant is used, and no special electrolytic solution is mixed.

FIG. 1 is a block diagram of a grinding apparatus of the present invention. The figure is composed of a main part 11 of a precision rotary surface grinder and a power supply device 12 for electrolysis. In the figure, the work material silicon 13 is fixed in a water tank 15 on a rotary table 14 and is submerged in a coolant 16 and ground by a CIFB-D grindstone 10. The entire grinding work surface of the grindstone 10 is wet with the coolant, and the grinding work surface is temporarily in partial contact with the work material. The positive (+) electrode (positive voltage) of the pulsed DC power supply 12 is connected to the power supply brush 17 applied to the outer circumference of the grindstone 10, and the negative (-) electrode (negative voltage) is connected to the copper wire 18 suspended in the coolant 16. Has been done. That is, electrolysis is always generated by making the necoolant itself a negative (-) pole. Before processing, use the WA stick grindstone (# 80, # 400)
Truing and dressing were performed by grinding with a CIFB-D grindstone (# 4000), and then silicon was ground under various electrolytic and grinding conditions. The surface roughness after grinding was measured with a reference length of 2.5 mm.

FIG. 2 is a graph showing the effect of the present invention. In advance, the CIFB-D grindstone was subjected to truing or the like with a WA stick grindstone, and electrolytic grinding of silicon was performed.
The feed rate is constant at 107 mm / min, the on-time of 2 μS,
It shows the change of the electrolytic ground surface roughness with a grinding distance of 1000 mm for four cases of maximum current values of 100, 120, 140 and 160 A, respectively, using a pulsed DC voltage with an off time of 2 μS. As is clear from the figure, in both cases, the surface roughness improves with the electrolytic grinding distance, and when the maximum current value is 140,160 A, Rmax 0.1-0.2 μm is achieved at a grinding distance of 700 mm or more, and the electrolytic effect It can be seen that the dressing of the CIFB-D grindstone according to is effective.

Subsequently, after the dressing effect, grinding was performed while applying electrolysis. FIG. 3 is a graph showing the electrolytic grinding characteristics. Using a pulse current voltage with an ON time of 1 μS and an OFF time of 1 μS, the maximum current value was maintained at 160 A, and the feed speed was 35 mm at a grinding distance of 1000 mm.
It is processed by setting 9,202,107,76,44 mm / min. From the figure, the surface roughness of electrolytic grinding is 359 mm / mi for high-speed feed.
Grinding surface of Rmax 0.4μm continues even at n, low speed feed 44mm / min
In, the mirror surface of Rmax 0.06-0.08 μm was realized. Although the maximum current value is set to 16 OA in the figure, electrolytic grinding using a CIFB-D grindstone can similarly finish the surface roughness even if the current value is lowered to about 10A.

As described above, according to the present invention, a very good mirror surface can be achieved. Further, the ground surface obtained by the device of the present invention is
Even if the work material is a brittle material, it exhibits a surface texture due to almost complete plastic flow and is a mirror surface. Since almost no brittle fracture occurred on this mirror surface, it was confirmed that few cracks remained on the surface layer.

The present inventors have obtained very good results not only for the silicon of the above-mentioned examples but also for ferrite and alumina, and the results are shown in the table below.

[Brief description of drawings]

1 is a configuration diagram of a grinding apparatus of the present invention, FIG. 2 is a graph showing an effect of electrolytic dressing of the present invention, FIG. 3 is a graph showing electrolytic grinding characteristics of the present invention, and FIG. 4A is Showing the protruding state of the abrasive grains on the magnet surface by the electrolytic dressing effect of the present invention, a schematic view of a grindstone cross section, FIG. 4B shows the removal of clogging by the dressing effect during the electrolytic grinding process of the present invention. Schematic diagram, FIG. 5A is a schematic diagram showing a cross-sectional shape before use of the CIFB-D grindstone, and FIG. 5B is a schematic diagram of a cross-sectional shape obtained by truing and dressing the CIFB-D grindstone with a WA stick grindstone. (Description of symbols) 11 …… Main part of precision rotary surface grinder, 12 …… Power supply unit for power supply, 13 …… Silicon work material, 14 …… Rotary table, 15 …… Coolant tank, 16 …… Coolant liquid , 17 ... Power supply brush, 18 ... Copper wire.

Claims (1)

[Claims] 1. A liquid receiving part for receiving a supplied weakly conductive grinding liquid, a metal bond grindstone using cast iron as a bonding material, and the entire grinding surface of the grindstone received by the liquid receiving part. A metal bond grind that is wetted inside and whose work surface is temporarily in partial contact with the work piece, and the grinding work surface of the metal bond grindstone is moved relative to the work piece to perform the grinding. A means for sliding the working surface on the ground surface of the work piece, and the metal bond grindstone as an anode, the electrode wetted by the grinding liquid as a cathode, and a pulse while the sliding is performed. A grinding apparatus comprising a pulsed DC power supply for applying a DC voltage.